In many image processing apparatuses for printing color images, to print at a high speed components (black, cyan, magenta, and yellow) that have undergone image processing, independent photosensitive drums 1, 2, 3, and 4 are physically laid out at predetermined intervals 5, 6, and 7 (to be referred to as drum pitches hereinafter), and a sheet surface 8 is conveyed in a predetermined direction to sequentially print the components, as shown in FIG. 1.
The operation will be described below in detail with reference to FIG. 2.
Image data 23 to 26 of the respective components input from an image input apparatus 10 to an image processing apparatus 11 undergo image processing operations 13 to 16, respectively.
FIG. 2 illustrates input images and output images in the same color space for the descriptive convenience, though the processing is substantially the same even when input images and output components have different color spaces (e.g., RGB inputs and CMYK outputs).
Since the image processing operations for the components are parallelly executed for each pixel, delay amounts generated by the drum pitches are adjusted by storage devices 17 to 19.
To adjust phase differences generated by the drum pitches, the outputs from the image processing operations 14 to 16 are stored in the storage devices 17 to 19, respectively, as needed.
A first output component 27 is output to a printer controller 12 without intervening any storage device because no phase adjustment is necessary for the photosensitive drum 1 of the printer, which prints first.
For a second output component 28, the image-processed data is stored in the storage device 17. In accordance with a read control signal 32 transmitted from a read control circuit 20, the data is read out from the storage device 17 and output to the printer controller 12. At this time, a phase difference corresponding to the drum pitch 5 is adjusted.
For a third output component 29, the image-processed data is stored in the storage device 18. In accordance with a read control signal 33 transmitted from the read control circuit 20, the data is read out from the storage device 18 and output to the printer controller 12. At this time, a phase difference corresponding to the drum pitch 6 is adjusted.
For a fourth output component 30, the image-processed data is stored in the storage device 19. In accordance with a read control signal 34 transmitted from the read control circuit 20, the data is read out from the storage device 19 and output to the printer controller 12. At this time, a phase difference corresponding to the drum pitch 7 is adjusted.
A print request signal synchronization circuit 36 and the read control circuit 20 will be described next with reference to FIGS. 2 and 3.
On the basis of a print request signal 31 from the printer controller 12, the image input apparatus 10 is activated. After image processing by the image processing apparatus 11, the printer controller 12 receives the output data 27 to 30 from the image processing apparatus 11 and prints them by the above-described method.
In such a case, to adjust a delay generated due to the physical characteristic of the electric wire that connects the printer controller 12 to the image processing apparatus 11 or the states of the printer controller 12 and image processing apparatus 11 operating by clocks of different frequencies, the print request signal 31 input from the printer controller 12 is synchronized by an image processing clock 22 and then input to the read control circuit 20. After the synchronization, the read control circuit 20 delays the read control signal 32 on the basis of the print request signal by a time corresponding to the period (drum pitch 5) in which the sheet surface is conveyed from the first photosensitive drum section 1 to the second photosensitive drum section 2, and transmits the delayed read control signal 32 to the storage device 17. Similarly, the read control circuit 20 delays the read control signal 33 on the basis of the print request signal by a time corresponding to the period (drum pitch 6) in which the sheet surface is conveyed from the first photosensitive drum section 1 to the third photosensitive drum section 3, and transmits the delayed read control signal 33 to the storage device 18. In addition, the read control circuit 20 delays the read control signal 34 on the basis of the print request signal by a time corresponding to the period (drum pitch 7) in which the sheet surface is conveyed from the first photosensitive drum section 1 to the fourth photosensitive drum section 4, and transmits the delayed read control signal 34 to the storage device 19.
The circuit that implements the image processing apparatus 11 shown in FIG. 2 cannot be mounted on a single semiconductor integrated circuit in some cases due to its scale. Additionally, in a monochromatic printing system, the image processing apparatus 11 is redundant and increases the cost. Due to the above reasons, the image processing apparatus is sometimes divided into two semiconductor integrated circuits 11A and 11B, as shown in FIG. 4.
The image processing apparatus is present physically as a plurality of semiconductor integrated circuits. In this case, however, when the print request signal input from the printer controller 12 is synchronized with an image processing clock by synchronization circuits 36A and 36B prepared in the respective integrated circuits of the image processing apparatuses, print request signals 35A and 35B after synchronization may have a phase difference. Hence, for example, the read control signal 33 which is expected to change at edge 1 in FIG. 5 may change at edge 2. This causes a color misregistration in the printed picture, resulting in degradation in image quality.